Railway track circuit apparatus



Dec. 15, 1936. A.'E. DODD RAILWAY TRACK CIRC UIT APPARATUS Filed May 51, 1953 IN WIN TOR E. Dada? Qjmf Arthur BY HIS A TTORNEY Patented Dec. 15, 1936 liitil hfi S'EATES PATENT @EFHQE RAILWAY TRACK CIRCUIT APPARATUS Application May 31, 1933, Serial No. 673,595

13 Qlaims.

My invention relates to railway track circuit apparatus, and has for an object the provision, in apparatus of this character, of a track relay combination which can be adjusted to provide as nearly as possible maximum shunting sensitivity under infinite ballast resistance condition. I accomplish this result by providing a track relay combination which may be adjusted to pick up and release on as nearly as possible the same values of current and voltage.

I will describe several forms of track circuit apparatus embodying my invention, and will then point out the novel features thereof in claims.

In the accompanying drawing, Fig. 1 is a diagrammatic View showing one form of track circuit apparatus embodying my invention. Figs. 2, 3, and 4 are diagrammatic views showing modifications of the track relay combination shown in Fig. 1 and also embodying my invention. Fig. 5 is a diagrammatic view showing a modified form of a portion of the apparatus shown in the foregoing figures.

Similar reference characters refer to similar parts in each of the views.

Referring first to Fig. 1, the reference characters I and l designate the track rails of a railway track, which rails are divided by insulated joints 2 to form a track section A-B.

At one end of this section a source of current C is connected across the rails through a current-limiting resistance 3, this source of current, as here shown, being a battery. Located at the other end of the section is a primary relay P and a secondary relay S.

The primary relay P is provided with a pickup circuit which is connected across the track rails and which passes from the lower rail l through the operating winding of relay P, and the back point of contact 6 of the secondary relay S to the upper rail i. It will be seen that this pickup circuit is closed when and only when the sec:- ondary relay S is released. The primary relay P is provided with a holding circuit which passes from the lower rail l through the operating winding of relay P, an adjustable resistance 9, and a front contact t of relay P, to the upper rail l. The secondary relay S is provided with a circuit which includes a battery l2 and a front contact 5 of the primary relay P, so that relay S is energized when and only when relay P is energized. When the armature of the secondary relay S is closed, a shunt is closed around the winding of relay P, which shunt includes the front point of contact 6 of relay S and an adjustable resistance Ill.

The primary relay P is preferably a relatively low resistance relay having normal pickup and releasing characteristics, and may, for example, be a standard l-ohm track relay. The secondary relay S is preferably a relatively high resistance relay having slow pickup characteristics, and may, for example, have a resistance of 50 ohms. A slow pickup secondary relay S is illustrated in Fig. 5. It will be understood, of course, that although a slow pickup relay is generally preferable when relay S controls a block signal of the usual type, nevertheless, in certain other applications of the invention it might be desirable to make relay S quick acting. For accomplishing the essential purpose of providing maximum shunting sensitivity to: which the invention is directed, the particular time elements of the relays P and S are of no special importance.

The operation of the apparatus shown in Fig. 1, is as follows: Relay P is normally energized by virtue of its holding circuit, and relay S is normally energized because its circuit is closed at contact 5 of relay P. When a train enters section A-B,' the shunt formed by the wheels and axles will reduce the voltage across the terminals of the operating winding of relay P to such value that this relay will release, and after the expiration of a given time interval following the opening of contact 5, determined by the slow releasing characteristic of relay S, the latter relay will release. The holding circuit for relay P will then be open at contact i, but the pickupcircuit for this relay will be closed at the back point of contact 6 of relay S. Relay P will continue to be released, however, as long as any part of the train remains in section A-B. When the entire train leaves this section, the voltage across the terminals of the operating winding of relay P will increase to a value above the pickup voltage of this relay, so that the relay P will then become energized. The holding circuit for relay P will then be closed at front contact 4, so that resistance 9 will be included in the circuit for the winding of this relay. Relay S will then close, thereby opening the pickup circuit for relay P and closing the shunt around the winding of relay P through the resistance Ill.

It will be observed from the foregoing that when the two relays P and S are released, the winding of the primary relay P is connected directly across the track rails, whereas when both of these relays are closed, the resistance 9 is included in series with the winding of relay P. This increases the shunting sensitivity of relay P, but also increases the resistance of the circuit including the winding of relay P. To compensate for this increase in resistance, the second resistance H3 is connected in multiple with the winding of relay P so that the resistance of the relay combination when relay P is closed may be substantially the same as the resistance of the winding of relay P alone.

The apparatus shown in Fig. 1 does not depend upon the adjustment of the track resistor 3, at the minimum ballast resistance, for the amount of flux reduction obtained in relay P when a train enters the section. The values of resistors 9 and H! can be vari d to provide for any spread between the pickup and release values of relay P. The parts are so adjusted that both the release current and the release voltage of relay P approach the pickup current and the pickup voltage of this relay, so that the relay combination approaches the ideal track relay, and, therefore, provides the maximum shunting sensitivity obtainable with a track circuit of any length.

Referring now to Fig. 2, the apparatus shown in this view is the same as that shown in Fig. 1, except that when relay S is closed, the resistor i0 is connected across the track rails i and Ea instead of across the terminals of the winding of relay P. The operation and characteristics of the apparatus shown in Fig. 2 will be the same as those of the apparatus shown in Fig. 1, the only difference being that the calculation of the values of resistors 9 and I0 is somewhat simpler with the apparatus shown in Fig. 2 than with the apparatus shown in Fig. 1.

In Fig. 3 a single resistor 9 is provided, all of which resistor is connected in multiple with the winding of relay P when this relay is closed. When relay S is closed, a portion of resistor 9 is connected across the track rails l and la, this portion, as here shown, being the portion between an intermediate point 15 and the righthand end of the resistor. In this instance, contact 6 is a continuity transfer contact, meaning that when the relay S closes, the front point of this contact closes before the back point opens.

Referring now to Fig. 4, the apparatus shown in this view is the same as that shown in Fig. 1, except that the shunt path around the winding of relay P including the resistor H] is omitted.

In each of the views the secondary relay S is provided with other contacts, such as l and 8, which may be used to control railway signals or any desired trafiic governing apparatus.

Although I have herein shown and described only a few forms of track circuit apparatus embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. In combination with a section of railway track and a source of current connected across the rails of said section, a primary relay and a secondary relay, a pickup circuit for said primary relay connected across the rails of said section and including a back contact of said secondary relay, a holding circuit for said primary relay connected across said rails and including a front contact of the primary relay, 2.

shunt around the operating winding of said primary relay including a front contact of said secondary relay and a resistance, and a circuit for said secondary relay including a front con tact of said primary relay.

2. In combination with a section of railway track and a source of current connected across the rails of said section, a primary relay and a secondary relay, a pickup circuit for said primary relay connected across the rails of said section and including a back contact of said secondary relay, a holding circuit for said primary relay connected across said rails and including a front contact of the primary relay and a resistance, a shunt around the operating winding of said primary relay including a front contact of said secondary relay and a second resistance, and a circuit for said secondary relay including a front contact of said primary relay.

3. In combination with a section of railway track and a source of current connected across the rails of said section, a primary relay and a secondary relay, a pickup circuit for said primary relay connected across the rails of said section and including a back contact of said secondary relay, a holding circuit for said primary relay connected across said rails and including a front contact of the primary relay, a shunt path connected across the rails of said section and including a front contact of said secondary relay and a resistance, and a circuit for said secondary relay including a front contact of said primary relay.

4. In combination with a section of railway track and a source of current connected across the rails of said section, a primary relay and a secondary relay, a pickup circuit for said primary relay connected across the rails of said section and including a back contact of said secondary relay, a holding circuit for said primary relay connected across said rails and including a front contact of the primary relay and a resistance, a shunt path connected across the rails of said section and including a front contact of said secondary relay and asecond resistance, and a circuit for said secondary relay including a front contact of said primary relay.

5. In combination with a section of railway track and a source of current connected across the rails of said section, a primary relay and a secondary relay, a pickup circuit for said primary relay connected across the rails of said section and including a back contact of said secondary relay, a holding circuit for said primary relay connected across said rails and including a front contact of the primary relay and a resistance, a shunt path connected across the rails of said section and including a front contact of said secondary relay and a portion of said resistance, and a circuit for said secondary relay including a front contact of said primary relay.

6. In combination with a section of railway track and a source of current connected across the rails of said section, a primary and a secondary relay, a pickup circuit for said primary relay connected across the rails of said section and including a back contact of said secondary relay, a holding circuit for said primary relay connected across said rails and including a front contact of the primary relay, a circuit for energizing said secondary relay including a front contact of said primary relay, and means including a resistor connected with the rails of said section and effective when said secondary relay is energized for decreasing the effectiveness of said holding circuit.

'7. In combination with a section of railway track and a source of current connected across the rails of said section, a primary and a secondary relay, a pickup circuit for said primary relay connected across the rails of said section and including a back contact of said secondary relay, a holding circuit for said primary relay connected across said rails and including a front contact of the primary relay, a circuit for energizing said secondary relay including a front contact of said primary relay, and means including a front contact of said secondary rely for increasing the current drawn from said source to thereby decrease the voltage effective in said holding circuit.

8. In combination with a section of railway track and a source of current connected across the rails of said section, a primary and a secondary relay, a pickup circuit for said primary relay receiving energy from the rails of said section and controlled by said secondary relay, a holding circuit for said primary relay also receiving energy from the rails of said section and including a contact of said primary relay, means controlled by said primary relay for energizing said secondary relay, and means effective when said secondary relay is energized for increasing the current drawn from said source to thereby decrease the energy received by said primary relay.

9. In combination with a section of railway track and a source of current connected across the rails of said section, a primary and a secondary relay, a pickup circuit for said primary relay receiving energy from the rails of said section and controlled by said secondary relay, a holding circuit for said primary relay also receiving energy from the rails of said section and including a contact of said primary relay and an impedance, means controlled by said primary relay for energizing said secondary relay, and means controlled by said secondary relay for connecting a second impedance with the rails of said section at such time as said holding circuit is effective for decreasing the amount of energy received by said primary relay over said holding circuit.

10. In combination with a section of railway track and a source of current connected across the rails of said section, a primary and a secondary relay, a pickup circuit for said primary relay receiving energy from the rails of said section and controlled by said secondary relay, a holding circuit for said primary relay also receiving energy from the rails of said section and including a contact of said primary relay and an impedance, means controlled by said primary relay for energizing said secondary relay, and means controlled by said secondary relay for connecting a second impedance with the rails of said section to thereby maintain the equivalent impedance of the primary relay load substantially constant irrespective of whether said pickup circuit or said holding circuit is effective.

11. In combination with a section of railway track and a source of currentconnected across the rails of said section, a primary and a secondary relay, a pickup circuit for said primary relay receiving energy from the rails of said section and controlled by said secondary relay, a holding circuit for said primary relay also receiving energy from the rails of said section and including a contact of said primary relay and an impedance, means controlled by said primary relay for energizing said secondary relay, and means controlled by said secondary relay for increasing the load supplied from the rails of said section at such time as said holding circuit is effective to thereby maintain the current delivered from said source to the rails of said section substantially constant irrespective of whether said pickup circuit or said holding circuit isv effective.

12. In combination with a section of railway track and a source of current connected across the rails of said section, a primary and a secondary relay, a pickup circuit for said primary relay receiving energy from the rails of said section and controlled by said secondary relay, a holding circuit for said primary relay controlled by the primary relay and normally receiving less energy from the rails of said section than is received by said pickup circuit, means controlled by said primary relay for energizing said secondary relay, and means eiiective when said secondary relay is energized for increasing the energy taken from the rails of said section by an amount which when added to the energy received by said holding circuit will substantially equal the energy received by said pickup circuit.

13. The method of rendering the shunting sensitivity of a track circuit having a source of current and a track relay connected therewith substantially independent of the track circuit length which comprises, normally supplying the track relay with holding energy which is smaller in amount than the pickup energy at times supplied to the track relay, and adding an increment of load to the track circuit at such time as the holding energy is effective to thereby make the current supplied from the track when the holding energy is efiective substantially the same as the current supplied therefrom when the pickup energy is effective.

ARTHUR E. DODD. 

